A technology of electrically connecting semiconductor chips by flip-chip bonding using bumps to allow connection portions to have multiple pins and lower capacity and increase the speed of data exchange between the semiconductor chips, as compared with connection using wire bonding in related art, has been devised (e.g., see PTL 1).
As an application of this technology, there is a technology of stacking a peripheral circuit on the light collection surface side of a surface type solid-state imaging device by flip-chip bonding. Performing flip-chip bonding on the light collection surface side of the surface type solid-state imaging device demands formation of bumps on the light collection surface. However, a light collection structure called on-chip lenses is formed on the light collection surface, and a lens material of an organic substance or the like that forms these on-chip lenses is stacked on the entire light collection surface including a peripheral circuit region as well as a pixel region. Therefore, to connect the bumps to electrode pads for bump connection formed on a semiconductor substrate, openings are made in the lens material and the bumps are formed on the openings.
In this case, the depth of the opening is increased by the thickness of the lens material, which makes it difficult to form the bumps with high precision. This applies not only to a solid-state imaging device but also to an element that uses a resin such as polyimide as a protective film.
As described above, in the case where a lens material exists in a region where bumps are formed, bonding of semiconductor chips cannot be performed easily.
Meanwhile, there is a solid-state imaging device in which a first semiconductor chip where photoelectric conversion elements and electrodes for connection and the like are formed and a second semiconductor chip where an A/D conversion circuit, a signal processing circuit, a logical operation circuit, and the like and electrodes for collection are formed are stacked by being made to face each other and being bonded to each other with bumps.
The number of pixels of a solid-state imaging device used for a camera or the like is normally several millions to several tens of millions and thus a large number of electrodes for connection are necessary; the electrodes for connection are arranged with high density of a pitch of several tens of micrometers.
To accurately connect the electrodes for connection arranged with high density, it is necessary to arrange alignment marks on each of the first semiconductor chip and the second semiconductor chip, and perform bump bonding while performing alignment precisely on the basis of the alignment marks.
Methods for bump bonding include a chip-on-chip bonding method (e.g., see PTL 2) and a chip-on-wafer bonding method (e.g., see PTL 3). The chip-on-chip bonding method, which is a method of bonding semiconductor chips in units of semiconductor chips, has low bonding efficiency and is not suitable for mass production.
The chip-on-wafer bonding method is a method of bonding a plurality of second semiconductor chips to a semiconductor wafer where first semiconductor chips are arranged in a matrix. Although this method improves bonding efficiency as compared with the chip-on-chip bonding method, in the case where the second semiconductor chips are bonded to the semiconductor wafer one by one, time taken for bonding of each semiconductor wafer is lengthened in proportion to the number of the second semiconductor chips to be bonded. This not only leads to a decrease in throughput, but also lengthens time for heat treatment necessary for bump bonding and thus increases heat load on the semiconductor wafer.
In the case where a plurality of second semiconductor chips are collectively bonded to a semiconductor wafer, although the number of times of bonding per semiconductor wafer is reduced and thus time taken for bonding is shortened, a design constraint of making the semiconductor chips have an axis of symmetry by mirror inversion in advance is necessary (e.g., see PTLs 4 and 5). However, since a solid-state imaging device obtains image signals from a lens image projected on the first semiconductor chip, physical arrangement, such as north, south, east, and west, cannot be changed easily. That is, it is difficult to impose a design constraint such as mirror inversion. Accordingly, bonding of semiconductor chips cannot be performed easily.